In the coming weeks and months, you might hear some well-meaning parents warn their children against swimming right after they eat.
The idea is that swimming after eating can cause muscle cramps or a side stitch. The preventative measure, usually, is to wait 30 minutes after eating before getting in the water.
It's unclear where this originally came from, and it seems to be losing some currency in recent years. But in case you still believe in it, here's the bottom line: there's absolutely no reason to believe that eating and swimming is particularly likely to cause cramps, stitches, or any other specific health problem.
Why eating and swimming is totally fine
The idea, apparently, is that eating right before swimming can trigger a stitch or muscle cramp — and in the worst-case scenario, these cramps can cause someone to drown. But there's no evidence to suggest that eating then swimming would cause either of these any more often than any other activity.
Muscle cramps are brought on by a few different factors, including muscle fatigue and dehydration. Some scientists believed reduced blood flow to muscles is also involved, though that's disputed.
If it were true, the blood sent to your stomach to aid in the digestion of a big meal could theoretically reduce blood flow to your muscles, making cramps a little more likely. But unless you're taking part in an extreme swimming challenge, doctors say you have more than enough blood to fuel your muscles and digest your food.
And even if you did get a muscle cramp, experts say it'd be extremely unlikely to disable and drown you. You might feel uncomfortable, but you'd be more than capable of swimming to shore, drinking a glass of water, and resting.
Side stitches — sudden, stabbing pains just below the ribcage that are scientifically known as exercise-related transient abdominal pains (ETAPs) — are more mysterious. There are a number of different explanations for how they're caused, why they seem to happen disproportionately during exercise.
But again, there isn't any data showing that ETAPs occur as a result of food and swimming specifically, and none of the hypothesized mechanisms would suggest that doing these things back-to-back would make them more likely.
The raw data backs this up. The CDC reports that, on average, there are about 10 fatal drownings in the US daily. They note that a number of common factors — such as alcohol use, lack of child supervision, and a failure of people who can't swim to wear life jackets — are to blame for the vast majority of these deaths. Eating before swimming isn't one of them.
So where did this idea come from?
It's unclear. Snopes.com traced it back as far as 1908, when the original edition of Scouting for Boys said:
First, there is the danger of cramp. If you bathe within an hour and a half after taking a meal, that is, before your food is digested, you are very likely to get cramp. Cramp doubles you up in extreme pain so that you cannot move your arms or legs — and down you go. You may drown — and it will be your own fault.
The belief persisted through the first half of the 20th century, then became particularly prominent during the 1950s and 60s. Over the past few years, it seems to have become less widely trusted, partly due to articles debunking it — like this one.